The engine immobiliser system is designed to prevent the vehicle from being stolen. This system uses a transponder key ecu that stores the key codes of authorized ignition keys. If an attempt is made to start the engine using an unauthorized key, the ecu sends a signal to the ecm to prohibit fuel delivery and ignition, effectively disabling the engine.

The transponder key coil receives this signal, the transponder key amplifier amplifies it, and then the signal is transmitted to the ecu. The ecu matches the key's id code with the vehicle's id code, which was previously registered in the ecu and then communicates the results to the ecm using sfi communication.
Engine immobiliser system
How to proceed with troubleshootingHow to proceed with troubleshooting
Hint:
Use these procedures to troubleshoot the tire pressure
warning system.
*: Use the intelligent tester.
Vehicle brought to workshop
Inspect battery voltage
Standard voltage:
11 to 14 v
If the voltage is below 11 v, recharge or replace the battery
before proceeding.
...
Oxygen (a/f) sensor pumping current circuit
Description
Refer to dtc p2195 (see page es-292).
Monitor description
The air-fuel ratio (a/f) sensor varies its output voltage in proportion to
the air-fuel ratio. If the a/f sensor
impedance (alternating current resistance) or output voltage deviates greatly
from the standard range ...
Terminals of ecu
Check power steering ecu
Hint:
Measurements cannot be performed on the c connector
side of the power steering ecu.
Measure the voltage and resistance of the
connectors.
If the result is not as specified, the ecu may have a
malfunction. ...